Abstract: 【Objective】 The effect of nitrate ( NO₃^--N ) and ammonium ( NH₄⁺-N) on the growth and nitrogen absorption kinetics of loquat seedlings was studied to determine the absorption and utilization of nitrogen forms and to provide a scientific basis for the management of loquat. 【Method】 Taking loquat seedlings as materials and using the ion depletion method, the loquat seedlings roots of different nitrate and ammonium absorption kinetics parameters were tested. The yellow soil with pH at 7.35 was used as the cultivation medium, and five different ratios of nitrate and ammonium were designed. The effect of different ratios of nitrate and ammonium on the growth and the root morphology were studied. 【Result】 At different NH₄⁺ and NO₃^- ion concentrations and ratios of ammonium nitrate in the nutrient solution, the regular pattern of the absorption of ammonium, nitrate and total nitrogen in the root system of loquat seedlings was followed with the Michaelis-Menten dynamic equation. No matter how the NH4+ and NO₃^- ion concentrations changed, the inherent potential absorption, affinity and roots of flow rate of loquat seedlings roots for NH₄⁺ absorption were greater than NO₃^-. Under the pure nitrate supply conditions, loquat absorption of NO₃^- did not get the promotion. During the treatment supplied different proportions of ammonium nitrate, with the increasing of the proportion of ammonium, total nitrogen for loquat seedlings roots of maximum uptake rate (I_max) and the root of the velocity (α) increased significantly, while the Michaelis constant value (K_m) significantly reduced. The I_max and α of these value declined and the K_m values increased with the increasing in the proportion of nitrate. The ratio of increasing in the proportion of ammonium can promote roots of loquat seedlings for nitrogen absorption, but increasing in the proportion of nitrate absorption of loquat roots has an adverse effect. Ammonium is the preferred absorption nitrogen forms of loquat. Under soil culture conditions, applying different proportions of ammonium nitrate, plant height, basal diameter, dry weight biomass, shoot ratio, root morphology index and total leaf area of loquat seedlings were different significantly. The proportion of ammonium fertilizer significantly increased plant height, basal diameter, dry weight biomass, root to shoot ratio, total leaf area and total root length, total surface area, total volume, average diameter, total count the number and root apical fractal dimension. In 100% of ammonium treatment, the above indicators were the largest, but in 100% of nitrate treatment, the above indicators were the smallest. 【Conclusion】 In a single source of nitrogen and different ratios of ammonium nitrate mixture for nitrogen conditions, the maximum absorption rates of loquat seedlings roots on NH₄⁺ were larger than NO₃^-, and the inflow rate of roots for NH₄⁺ were faster than NO₃^-, and the affinity of roots for NH₄⁺ were stronger than NO₃^-, and showed significant absorption preferences for ammonium. Loquat likes ammonium nutrition absorption characteristics, which is the preferred form of loquat absorption. So ammonium can obviously promote the growth development of loquat seedlings and strengthen the loquat seedlings for nitrogen uptake, but nitrate can inhibit the growth of loquat seedlings. Under the conditions of mixed supply of ammonium and nitrate, adding ammonium could promote the growth development of loquat seedlings.

Key words: loquat, nitrate, ammonium, growth, absorption kinetics